JPH1090047A - Weighing meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove error with ease by calculating change amount of enumerated value due to creep as a function of a read enumerated value and that from loaded point till measurement time point, and taking as a load value after removing the change amount from the read enumerated value. SOLUTION: A correction amount Δ of creep error value occurring at each measurement time is represented in Δ=-(A×N<2> +B×N+C)/(D×T<2> +T+E). Where, Δ is creep correction amount, N is an enumerated value obtained with a load, T is a time period under load, and A-E are a constant which is specific to a weighing meter. A display value NW at a time TN is obtained form equation NW=NTN-(ΔNT1 +ΔNT2 ...+ΔNTN)(ΔNTn is creep error value at time TN). With a temperature censor and an A/D converter, a temperature at measurement is obtained, and t-t0 =Δt, where (t) is temperature at measurement and t0 is temperature constant. While, A=aΔt, B=bΔt, C=cΔt, D=dΔt, E=eΔt, constants A-E are calculated. a-e, tδ0Χ are obtained according to the material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electronic weighing scale and a method for maintaining the measurement accuracy.

[0002]

2. Description of the Related Art The material and shape of a strain-generating body that balances a load, the material and thickness of an insulating material attached to the strain-generating body and serving as a base of a strain gauge that converts the amount of strain of the strain-generating body into an electric quantity, and Each element of the scale was selected and adjusted so that the elements with different effects and effects due to creep, such as the pattern shape of the strain resistance, cancel each other out, and the apparent creep becomes zero as a whole. .

[0003] In order to eliminate the creep error by combining the elements having different effects and effects due to creep, the materials to be used are severely restricted, and the combination requires a great deal of time and money. It took a lot of time and money to design according to the specifications of the scale each time the specifications of the weighing differed.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a scale which is simpler, less expensive and free of creep errors.

[0005]

Means for Solving the Problems The change in the count value due to creep is calculated as a function of the read count value and the time from when the load is applied to the time of measurement, and the change in the count value due to creep is calculated from the read count value. The value from which is removed is defined as the weight of the load.

[0006]

[Action] The count value obtained when a load is applied is
It is known that it changes over time.
This is because the deformation due to the load of the flexure element is actually due to "pseudoelasticity", and it becomes a state close to plastic deformation, and the deformation progresses as time passes. This tendency is conspicuous in the strain gauge base, which is a resin material serving as an insulator.

FIG. 2 shows a change in the count value when a certain load W is applied. Count value N _{T0 of} moment T _{0 when} load is applied
Is a true value, the error increases as time elapses, and the rate of increase decreases as time elapses. Although the rate of this increase is roughly proportional to the reciprocal of the time with reference to T ₀ , there is a strict difference, and a term of the square of the reciprocal is required. That is, when the error produced by T ₁ and .DELTA.N _T1, the proportionality constant at the K ΔN _T1 = N _T1 -
Represented by _{N T0 = K / (DT 1} 2 + T 1 + E). D and E are constants specific to each measuring instrument. The following Similarly _{ΔN T2 = N T2 -N T1 =} K / (DT 2 2 + T 2 + E) ΔN T3 = N T3 -N T2 = K / (DT 3 2 + T 3 + E) ΔN T4 = N T4 -N T3 = It can be calculated as K / (DT ₄ ² + T ₄ + E).

The true value at T ₁ is the creep error Δ
Since a value obtained by subtracting the N _T1, creep correction amount -DerutaN _T1
Can be represented by That is, the display value N _W is N _W = N _T1 −ΔN _T1 = N _T1 − (N _T1 −N _T0 ) = N _T0 , and it is understood that the display value N _W is a true value. Correction amount for the display value N _W at T ₄ will that the sum therebetween creep correction amount. N _W = N _T4 − (ΔN _T1 + ΔN _T2 + ΔN _T3 + ΔN _T4 ) = N
_T0 That is, creep error value at T _n is expressed by _{ΔN Tn = N Tn -N Tn-} 1 = K / (DT n2 + T n + E), the display value at T _n is N _W = N _Tn - ( ΔN _T1 + ΔN _T2 +... + ΔN _Tn-1 + ΔN
_Tn ).

The proportional constant K varies depending on the load. Each load and the amount of creep error during a certain time after the load are shown in FIG.
The relationship is shown in The creep error increases as the load increases, at a rate larger than the proportional to the load, and K = AW ²
+ BW + C. (W: Load, A, B, C:
Constant) The load is determined using a count value N obtained by the load, and the proportional constant K is determined as K = AN ² + BN + C. That is, the creep correction amount can be obtained by Δ = − (A × N ² + B × N + C) / (DT ² + T + E).

[0010]

FIG. 1 is a block diagram showing a bright embodiment according to the present invention. The creep correction formula for obtaining the creep error value generated at each measurement time is represented by Δ = − (A × N ² + B × N + C) / (DT ² +
The creep correction amount is calculated as (T + E), (Δ: creep correction amount, N: count value obtained by load, T: time when load is applied, A, B, C, D, E: constants specific to weighing scale ) display value at T _n, N _W and _{N W = N Tn - (ΔN} T1 + ΔN T2 + ...... + ΔN Tn-1 + ΔN
_Tn ) is obtained by calculation. Using a temperature sensor and A / D converter, with the temperature at the time of measurement, the temperature at the time of measurement t, the temperature constant t ₀ Distant, A = a (t-t 0), B = b (t −
t ₀ ), C = c (t−t ₀ ), D = d (t−t ₀ ), E =
e (t−t ₀ ), the above constants, A, B, C, D and E
Is obtained by calculation. a, b, c, d, e and t ₀
Is a value determined according to the actual material. Also,
A, B, C, D, and E at each temperature are stored in advance, and A, B, and
It is effective to call and use C, D and E.

[0011]

As described above, the true value of the load can be obtained by obtaining the creep error of the load sensor as a function of the load value and the load time, and correcting the read value. The scale can be designed according to the use and use of the scale with few restrictions, and a scale capable of accurate measurement with corrected creep value can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a count value and time when a load is applied.

FIG. 3 is a diagram showing a relationship between a load and a creep after a certain time after the load.

Claims (3)

[Claims] In a weighing scale that converts a load into a count value and weighs it, a time during which the load is applied is measured, and a creep correction formula including a term of the obtained count value and a time required for the measurement is calculated. Wherein the value obtained from the correction formula is used as a creep error correction value generated at each time, and a value obtained by successively adding the count value and the creep error correction value is used as a display value. . 2. A creep correction equation for calculating a creep error value generated at each time is represented by Δ = − (A × N ² + B × N + C) /
^2. The weighing scale according to claim 1, wherein (DT ² + T + E). In the above correction formula, Δ is the amount of creep correction, N is the count value obtained by the load, T is the time during which the load is applied, and A, B, C, D, and E are constants specific to the weighing scale, respectively. It is. 3. The method according to claim 2, further comprising means for obtaining the temperature of the load sensor, wherein the constants A, B, C, D and E of the creep correction equation are functions of the temperature at the time of measurement. Weight scale as described.